An app that writes memory byte at time instead of blitting, probably won't.
Still, if that app draws a framebuffer texture of, say, 320*200, this texture could be scaled, rotated, blended or filtered almost for "free", using compositing or OpenGL.

So it really depends what the application is doing.

The above is an answer from one of the AmigaOS4 SDL2 porters.

I guess it would be a lot of work supporting those render targets?
I'm just asking because it would probably speed up rendering on SDL quite a lot, but that's just my guess.

I'd also like to know what exactly is covered by the OpenGL renderer option.
Is it only the launcher or does OpenGL take over rendering the game screen as well?

I was trying to build with ogles2, but it throws errors on shader compilation when i start ScummVM (which is kind of normal, given my platforms unfinished gles2 implementation) and an assertion, probably because of said erroneous shader compilation.